In Taiwan, the real estate brokerage industry consists of advertising sales agents and brokers. Brokers are responsible for the sale of finished or newly finished houses. Since 1969, the presale house system has created a need for advertising sales agents, who primarily sell unfinished houses or newly finished houses on behalf of developers. This study is based on the traditional service quality model but integrates the transaction costs model (TCM), legal regulations (LR), and formal control mechanisms (FCMs) as moderators to assess the evaluation of the advertising sales agents service quality. First, the results show that the agency problems will affect the transaction costs, the service quality and behavioral intentions; second, transaction costs will affect service quality and behavioral intentions. Moreover, the better quality of service provided by the real estate advertising sale agents, the higher the satisfaction and behavioral intentions; finally, the LR can reduce transaction costs. The results also show that an FCM negatively moderates the relationship between agency problems and transaction costs.